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United States Patent |
6,130,290
|
Troy
,   et al.
|
October 10, 2000
|
Impact modifier for amorphous aromatic polyester
Abstract
Impact modifiers that produce transparent, high Dynatup impact strength
blends with amorphous, aromatic polyesters are described. The impact
modifiers are core-shell polymers with (A) a core composed principally of
rubbery polymers, such as copolymers of diolefins with vinyl aromatic
monomers, such as copolymers of butadiene with styrene, (B) an
intermediate stage composed principally of hard polymers, such as polymers
or copolymers of vinyl aromatic monomers, and (C) a shell composed
principally of vinyl aromatic copolymers that contain hydroxyl functional
groups or their equivalents (e.g. styrene/hydroxyalkyl (meth)acrylate
copolymers).
Inventors:
|
Troy; Edward Joseph (Bristol, PA);
Ryan; Joseph John (Yardley, PA)
|
Assignee:
|
Rohm and Haas Company (Philadelphia, PA)
|
Appl. No.:
|
277002 |
Filed:
|
March 26, 1999 |
Current U.S. Class: |
525/63; 525/64; 525/67; 525/71; 525/902 |
Intern'l Class: |
C08G 063/48; C08G 063/91; C08L 051/08; C08L 051/00; C08L 053/00 |
Field of Search: |
525/71,902,64,67,63
|
References Cited
U.S. Patent Documents
3793402 | Feb., 1974 | Owens.
| |
3971835 | Jul., 1976 | Myers et al.
| |
4034013 | Jul., 1977 | Lane.
| |
4707513 | Nov., 1987 | Baer.
| |
4713268 | Dec., 1987 | Carson.
| |
5321056 | Jun., 1994 | Carson et al.
| |
5322663 | Jun., 1994 | Lai et al.
| |
5438099 | Aug., 1995 | Fischer et al.
| |
5534594 | Jul., 1996 | Troy et al.
| |
5560994 | Oct., 1996 | Kitaike et al.
| |
5563227 | Oct., 1996 | Kitaike et al.
| |
5576394 | Nov., 1996 | Chao et al.
| |
5599854 | Feb., 1997 | Troy et al.
| |
5652306 | Jul., 1997 | Meyer et al.
| |
5668215 | Sep., 1997 | Chao et al.
| |
Foreign Patent Documents |
597275 B1 | Oct., 1993 | EP.
| |
93/21274 | Oct., 1993 | WO.
| |
Other References
JP 54-48850 (English Translation), Apr. 1979.
|
Primary Examiner: Niland; Patrick D.
Attorney, Agent or Firm: Rosedale; Jeffrey H.
Parent Case Text
This application claims benefit of Provisional Application Ser. No.
60/083,432 filed Apr. 29, 1998.
Claims
We claim:
1. A core-shell impact modifier composition comprising
(A) from about 15 to about 85 parts of a core comprising from about 40 to
about 60 percent by weight of units derived from at least one vinyl
aromatic monomer, from about 20 to about 60 percent by weight of units
derived from at least one 1,3-diene, up to about 10 percent by weight of
units derived from at least one copolymerizable vinyl or vinylidene
monomer, and up to about 5 percent by weight of at least one graft-linking
or cross-linking monomer;
(B) from about 10 to about 50 parts of an intermediate stage comprising at
least about 25 percent by weight of units derived from at least one vinyl
aromatic monomer; and
(C) from about 5 to about 35 parts of an outer shell comprising from about
2 to about 40 percent by weight of units derived from at least one
hydroxyalkyl (meth)acrylate, from about 60 to about 98 percent by weight
of units derived from at least one vinyl aromatic monomer, and up to about
25 percent by weight in the shell of units derived from one or more
copolymerizable vinyl or vinylidene monomer, and up to about 5 percent by
weight of units derived from at least one graft-linking or cross-linking
monomer;
the core-shell impact modifier having a refractive index of from about 1.55
to about 1.60.
2. The core-shell impact modifier of claim 1 where the core (A) comprises
(1) from about 10 to about 50 parts based upon the impact modifier of an
inner stage comprising at least 80 percent of units derived form at least
one vinyl aromatic monomer, up to about 20 percent of units derived from
at least one other copolymerizable vinyl or vinylidene monomer, up to
about 20 percent by weight of units derived from at least one 1,3-diene,
and up to about 5 percent by weight of units derived from at least one
graft-linking or cross-linking monomer; and
(2) from about 5 to about 75 parts based upon the impact modifier of an
outer stage comprising up to about 60 percent by weight of units derived
from a vinyl aromatic monomer, at least about 30 percent by weight of
units derived from at least one 1,3-diene, up to about 10 percent by
weight of units derived from at least one copolymerizable vinyl or
vinylidene monomer, and up to about 5 percent by weight of units derived
from at least one graft-linking or cross-linking monomer.
3. The core-shell impact modifier of claim 1 where the outer shell (C)
comprises a plurality of stages.
4. The core-shell impact modifier of claim 1, 2 or 3 where the vinyl
aromatic monomer is selected from styrene, para-methyl styrene,
alpha-methyl styrene, chlorostyrene, vinyl toluene, bromostyrene,
dibromostyrene, tribromostyrene, iso-propenyl napthalene, or vinyl
naphthalene, and where the 1,3-diene is butadiene.
5. The core-shell impact modifier of claim 1, 2 or 3 where the hydroxyalkyl
(meth)acrylate is selected from hydroxyethyl (meth)acrylate or
hydroxypropyl (meth)acrylate.
6. A clear amorphous blend comprising:
(A) at least one amorphous aromatic polyester or copolyester having a
refractive index of from about 1.55 to about 1.60; and
(B) the composition of claim 1, 2 or 3;
at a weight ratio of about 99/1 to about 70/30.
7. Articles produced from the blend of claim 6 under conditions that
maintain the polyester in an amorphous condition.
Description
BACKGROUND
The present invention relates to an impact modifier composition which
provides an improved balance of impact resistance and optical clarity to
amorphous aromatic polyester resin (hereafter referred to as polyester).
More specifically, the present invention concerns an impact modifier
composition which contains a rubbery core, an intermediate hard stage, and
a shell containing a hydroxyl group or another functional group which acts
in a similar manner as the hydroxyl group.
Polyesters (e.g., polyethylene terephthalate, polybutylene terephthalate,
etc.) exhibit various excellent properties such as resistance to
temperature, chemicals, weathering, radiation and burning and also exhibit
excellent clarity (in amorphous form), reasonable cost, as well as
moldability. Accordingly, polyesters are used for various purposes (e.g.,
fibers, films, molded and extruded products, etc.). The impact resistance
of the polyester, however, is less than satisfactory. Plastics such as
poly (butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET)
have insufficient impact strength, and many attempts have been made to
improve the impact strength. Many agents have been proposed to improve the
impact strength. These are added to resins and subjected to melt-blending.
Various attempts have been made using conventional fibrous inorganic
fillers (e.g., glass fiber, asbestos fiber, etc.) to improve the impact
resistance of polyester. Even when these methods are implemented, however,
the impact resistance improvement is less than satisfactory and clarity in
amorphous polyesters is adversely affected.
Various techniques wherein rubbery polymers or rubber- containing polymers
are mixed with polyesters have been developed to improve the impact
resistance of polyesters and thermoplastic materials. Specifically,
certain core-shell polymers comprising a core made of rubbery polymer and
a shell, around the core, made of a glassy polymer are excellent agents
for improvement of impact strength of polyesters where clarity is not an
object.
When these prior art methods are used, the polyester resin generally
exhibits poor compatibility with the shell of the rubber-containing
polymer, and therefore impact resistance is not fully optimized. Even when
these prior art core-shell modifiers are added to amorphous polyesters and
found to produce ductile, notched breaks, the clarity of amorphous
polyester resins is destroyed. An amorphous polyester may contain a small
amount of crystallinity, but the level must be low enough so that clarity
is not adversely affected. Further, although the polyester may be
crystallized under certain conditions, in the present invention the
molding and cooling conditions are such that crystallization (and loss of
clarity) is avoided.
Lane, U.S. Pat. No. 4,034,013 teaches core/shell polymers functionalized
with an epoxy group, such as a shell of methyl methacrylate/glycidyl
methacrylate, to improve the melt strength of polyesters. Although Lane
broadly teaches butadiene-based elastomers with optional minor amounts of
styrene in the core and teaches styrene as a major component of the outer
stage, she does not teach or suggest a solution to preparing an efficient
impact modifier which will retain clarity in the amorphous polyester.
Kishimoto et al., Japanese Kokai 54-48850, disclose butadiene-based
core/shell polymers with hydroxyalkyl groups in the shell portion as
modifiers for crystalline polyesters, such as poly(butylene
terephthalate), but do not teach the means to modify such core/shell
polymers to make them useful as impact modifiers in clear, amorphous
polyesters.
Carson et al., U.S. Pat. No. 5,321,056 teaches impact modifiers which
produce transparent, high notched Izod impact strength blends with
amorphous aromatic polyesters. Carson's impact modifiers are core-shell
polymers with cores comprised mainly of rubbery polymers of diolefins and
vinyl aromatic monomers and shells comprised mainly of vinyl aromatic
monomers and monomers containing a hydroxyl group. Although Carson
provides for significantly improved impact strength of clear, amorphous
aromatic polyester, a need still exists for a modifier that can provide an
improved balance of properties between impact strength and optical
clarity. Specifically, a need exists to reduce or eliminate the
blue/yellow hue or tint that often results from blending such modifiers in
amorphous aromatic polyester resins.
The object of the present invention is to provide a composition for
improving the impact strength of polyesters, such as PET or PET
copolyesters, when they are processed into clear, tough objects while
retaining their amorphous nature. It is another objective that said
composition provide improved impact properties without reducing the
transparency of amorphous polyesters. A further objective is that the
composition provide reduced blue/yellow hue, while maintaining desirable
impact and transparency characteristics. Another object is to provide a
composition which will also overcome the embrittlement caused by physical
aging which commonly occurs in amorphous aromatic polyesters when
conditioned at temperatures approaching glass transition temperature (Tg).
A still further object is to provide clear amorphous extrusion/melt shaped
or injection molded PET or PET copolyester articles.
STATEMENT OF INVENTION
In the present invention, impact strength of amorphous aromatic polyesters
is increased substantially by the addition of small amounts of certain
core-shell modifiers which disperse very readily in aromatic polyesters
and do not detract from clarity. Additionally, the present invention
provides an improved balance of impact resistance and optical properties
over previously known compositions. Specifically, the present invention
provides impact modifiers that substantially reduce the blue/yellow hue of
impact-modified clear amorphous aromatic polyesters. These and other
objects as will become apparent from the following disclosure are achieved
by the present invention.
The impact modifier composition of this invention is a core-shell polymer
with (A) a rubbery core such as a copolymer containing a diolefin,
preferably a 1,3-diene, (B) an intermediate stage comprised mainly of a
hard polymer such as a polymer containing a vinyl aromatic monomer, and
(C) a shell comprised mainly of a vinyl aromatic monomer (such as
styrene), and hydroxyalkyl (meth)acrylate or, in the alternative, another
functional monomer which acts in a manner similar to the hydroxyalkyl
(meth)acrylate).
The impact modifier of the present invention comprises:
(A) from about 15 to about 85 parts of a core stage comprising from about
40 to about 60 percent by weight of units derived from a vinyl aromatic
monomer, from about 20 to about 60 percent by weight of units derived from
at least one 1,3-diene, up to about 10 percent by weight of units derived
from at least one copolymerizable vinyl or vinylidene monomer, and up to
about 5 percent by weight of at least one graft-linking or cross-linking
monomer;
(B) from about 10 to about 50 parts of an intermediate stage comprising at
least about 25 percent by weight of units derived from a vinyl aromatic
monomer; and
(C) from about 5 to about 35 parts of an outer shell comprising from about
2 to about 40 percent by weight of units derived from at least one
hydroxyalkyl (meth)acrylate, from about 60 to about 98 percent by weight
of units derived from at least one vinyl aromatic monomer, and up to about
25 percent by weight in the shell of units derived from one or more
copolymerizable vinyl or vinylidene monomer, and up to about 5 percent by
weight of units derived from at least one graft-linking or cross-linking
monomer.
A further variation of the impact modifier structure is to provide within
the core (A): (1) an inner hard stage and, (2) an outer rubbery stage. The
inner hard stage comprises at least 80 percent of units derived form at
least one vinyl aromatic monomer, up to about 20 percent of units derived
from at least one other copolymerizable vinyl or vinylidene monomer, up to
about 20 percent by weight of units derived from at least one 1,3-diene,
and up to about 5 percent by weight of units derived from at least one
graft-linking or cross-linking monomer.
The outer rubbery stage comprises up to about 60 percent by weight of units
derived from a vinyl aromatic monomer, at least about 30 percent by weight
of units derived from at least one 1,3-diene, up to about 10 percent by
weight of units derived from at least one compolymerizable vinyl or
vinylidene monomer, and up to about 5 percent by weight of units derived
from at least one graft-linking or cross-linking monomer.
As used throughout this document, the term "stage" is intended to encompass
its broadest possible meaning, including the meaning conveyed in prior art
such as U.S. Pat. No. 3,793,402, U.S. Pat. No. 3,971,835, U.S. Pat. No.
5,534,594, and U.S. Pat. No. 5,599,854, which offer various means for
achieving "staged" polymers.
Another aspect of the invention is the blending of the impact modifier
composition with at least one aromatic polyester and/or copolyester at a
weight ratio of about 99/1 to about 70/30 of polyester/impact modifier,
the polyester remaining amorphous. A still further aspect of the invention
comprises molded parts, bottles, sheet, films, pipes, foams, containers,
profiles, or other articles prepared in accordance with the
above-mentioned compositions and blends.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that certain core-shell impact modifiers produce clear,
and unexpectedly tough blends with amorphous aromatic polyesters. These
modifiers produce a large increase in impact strength, while maintaining
excellent optical clarity of the polyesters. These modifiers have (A) a
core composed principally of rubbery polymers, such as copolymers of
diolefins with vinyl aromatic monomers, such as copolymers of butadiene
with styrene, (B) an intermediate stage composed principally of hard
polymers, such as polymers or copolymers of vinyl aromatic monomers, and
(C) a shell composed principally of vinyl aromatic copolymers that contain
hydroxyl functional groups or their equivalents (e.g. styrene/hydroxyalkyl
(meth)acrylate copolymers). For example, the core-shell impact modifiers
(i.e. "modifiers") which give this unexpected result contain shells
derived from copolymers of vinyl aromatic monomers with certain
hydroxyalkyl (meth)acrylates, for example, hydroxyethyl (meth)acrylate
(HEMA), hydroxypropyl (meth)acrylate (HPMA), 4-hydroxybutyl acrylate,
ethyl alpha-hydroxymethylacrylate, or hydroxyethyl acrylate (HEA), or
other copolymerizable monomers containing one or more hydroxyl groups,
such as allyl cellosolve, allyl carbinol, methylvinyl carbinol, allyl
alcohol, methallyl alcohol, and the like. Also included are other monomers
which function in a similar manner, for example, glycidyl methacrylate
(GMA), 3,4-epoxybutyl acrylate, acrylonitrile, methacrylonitrile,
beta-cyanoethyl methacrylate, beta-cyanoethyl acrylate, cyanoalkoxyalkyl
(meth)acrylates, such as omega-cyanoethoxyethyl acrylate, or
omega-cyanoethoxyethyl methacrylate, (meth)acrylamides, such as
methacrylamide or acrylamide, N-monoalkyl (meth)acrylamides, such as
N-methylacrylamide or N-t-butylacrylamide or N-ethyl (meth)acrylamide, or
vinyl monomers containing an aromatic ring and an hydroxyl group,
preferably non-phenolic, such as vinylphenol, para-vinylbenzyl alcohol,
meta-vinylphenethyl alcohol, and the like. Styrene homopolymer and other
styrene copolymers and terpolymers, such as styrene/methyl methacrylate
are very much less effective.
The monomer concentrations in the core, intermediate stage and shell of the
modifier composition are adjusted to provide a refractive index (RI) to
match that of the polyesters with which they are blended (i.e. about 1.55
to about 1.60). This produces a clear blend under processing conditions
which will maintain the polyester in its amorphous form. Almost all
rubbery polymers (e.g. cores) have RI's well below this range. Therefore
it is necessary that the rubber phase concentration of the impact modifier
composition be kept relatively low and the other components of the
modifier be used to bring the RI into the desired range. However, the
impact strength obtainable with a given concentration of any core-shell
impact modifier tends to vary directly with the amount of rubber polymer
in the modifier. This means that high RI modifiers having low rubber
contents have to be exceptionally efficient to produce good toughening.
From a practical standpoint the most desirable monomer to produce rubbery
polymer for this application is butadiene whose homopolymer has a RI=1.52.
It has the best combination of RI, cost, stability, and processability.
For the same reasons, styrene is the most desirable component for the rest
of the modifier. However, even if butadiene and styrene were the only
components of the modifier, a butadiene/styrene ratio ranging from about
50/50 to 20/80 would be required for the modifier RI to be in the 1.55 to
1.60 range needed for matching the RI's of amorphous, aromatic polyesters.
One skilled in the art of impact modification would expect a 50%
concentration of butadiene to be very low for good core-shell impact
modifier efficiency. The results found herein for modification of
polyesters with such functionalized "rubber-poor" modifiers are
surprisingly good.
In response to the need to match RI's of amorphous aromatic polyesters and
simultaneously have excellent impact modifier efficiency, U.S. Pat. No.
5,321,056 reports that when low concentrations of certain hydroxyalkyl
(meth)acrylates are copolymerized with aromatic vinyl monomers to form the
shell of core-shell impact modifiers having RI's in the 1.55 to 1.58
range, very high notched Izod impact strengths are obtained with amorphous
polyesters at 30% or lower modifier loadings, and preferably at from about
5 to about 20% loadings. Substitution of the hydroxyalkyl methacrylate
with other functional monomers promoting compatibility of the shell with
the polyester will give similar results in impact improvement and
maintenance of clarity. The modifier composition of the present invention
provides improved optical properties over the polymers reported in U.S.
Pat. No. 5,321,056, while maintaining the reported excellent impact
modifier efficiency of the compositions.
The requirement for a "rubber-poor" modifier can be relaxed somewhat if the
vinyl aromatic monomer is changed from styrene, vinyl toluene,
para-methylstyrene, monochlorostyrene and the like to one of high
refractive index, viz., the polybrominated vinyl aromatics or the
polycyclic vinyl aromatics.
The core of the impact modifier composition of the present invention is a
rubbery polymer and generally comprises a copolymer of butadiene and a
vinyl aromatic monomer. The rubbery polymer may include diene rubber
copolymers (e.g., butadiene-styrene copolymer,
butadiene-styrene-(meth)acrylate terpolymers,
butadiene-styrene-acrylonitrile terpolymers, isoprene-styrene copolymers,
etc.). Of the afore-mentioned rubbery polymers, those which can be
produced as a latex are especially desirable. In particular, a
butadiene-vinyl aromatic copolymer latex obtained as a result of emulsion
polymerization is preferred. In the core, a partially crosslinked polymer
can also be employed if crosslinking is moderate. Further, at least one of
a cross- or graft-linking monomer, otherwise described as a
multi-functional unsaturated monomer, can also be employed. Such monomers
include divinylbenzene, diallyl maleate, butylene glycol diacrylate, allyl
methacrylate, and the like.
The ratio of comonomers in the core depends on the desired core-shell ratio
and hardness of the rubber phase. The ratio range of butadiene to the
vinyl aromatic in the core polymer is 70/30 to 20/80 (parts by weight). If
the quantity of butadiene is below 20 parts by weight, it is difficult to
improve the impact resistance. If the quantity of butadiene exceeds 70
parts by weight, on the other hand, it is difficult to obtain a high
enough RI modifier to match that of the polyester, unless the vinyl
aromatic monomer is of high refractive index and selected from the
polybrominated or polycyclic monomers described above. Optionally, a small
concentration, from about 0.01 up to about 5, and preferably from about
0.1 up to about 2 percent, by weight of a crosslinking monomer, such as
divinyl benzene or butylene glycol dimethacrylate is included, and
optionally about 0.01 to about 5 percent by weight of a graftlinking
monomer for tying the core and shell together, such as allyl maleate may
be included in the rubbery core polymer. Further examples of crosslinking
monomers include alkanepolyol polyacrylates or polymethacrylates such as
ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene
glycol diacrylate, oligoethylene glycol diacrylate, oligoethylene glycol
dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane
dimethacrylate, trimethylolpropane triacrylate or trimethylolpropane
trimethacrylate, and unsaturated carboxylic acid allyl esters such as
allyl acrylate, allyl methacrylate or diallyl maleate.
As the intermediate stage of the impact modifier composition, hard polymers
or copolymers of vinyl aromatic monomers are preferred. Generally,
polymers or copolymers with a Tg above room temperature can be used.
Examples of suitable vinyl aromatic monomers include vinyl aromatic
monomers such as styrene, alpha-methyl styrene, para-methyl styrene,
chlorostyrene, vinyl toluene, dibromostyrene, tribromostyrene, vinyl
naphthalene, isopropenyl naphthalene, divinyl benzene and the like.
As the shell of the impact modifier composition, a
hydroxyl-group-containing monomer is preferred to be employed. When a
hydroxyl group is introduced to the shell polymer, a vinyl monomer
containing an active double-bond segment and a hydroxyl group (hereafter
referred to as hydroxyl-group-containing monomer) is copolymerized with
another copolymerizable vinyl monomer. Examples of the aforementioned
hydroxyl-group-containing monomers include hydroxyalkyl (meth)acrylate or
alpha-hydroxymethylacrylate esters, such as hydroxyethyl (meth)acrylate,
hydroxypropyl (meth)acrylate, or ethyl hydroxymethylacrylate, allyl
derivatives of hydroxyl-group containing compounds, such as allyl
cellosolve, allyl carbinol, methylvinyl carbinol, allyl alcohol, methallyl
alcohol, and the like, vinylphenol, para-vinylbenzyl alcohol,
meta-vinylphenethyl alcohol, and the like.
Although the hydroxyalkyl (meth)acrylate monomers are preferred for reasons
of safety in handling (over the nitrile-containing monomers) or
availability (over other monomers taught herein), other monomers which
function in a similar manner may be employed, for example, glycidyl
methacrylate (GMA), 3,4-epoxybutyl acrylate, acrylonitrile,
methacrylonitrile, beta-cyanoethyl methacrylate, beta-cyanoethyl acrylate,
cyanoalkoxyalkyl (meth)acrylates, such as omega-cyanoethoxyethyl acrylate,
or omega-cyanoethoxyethyl methacrylate, (meth)acrylamide, or N-monoalkyl
(meth)acrylamide and the like.
Vinyl aromatic monomers to be copolymerized with the aforementioned
hydroxyl-group-containing monomers include vinyl aromatic monomers such as
styrene, alpha-methyl styrene, para-methyl styrene, chlorostyrene, vinyl
toluene, dibromostyrene, tribromostyrene, vinyl naphthalene, isopropenyl
naphthalene, and the like. The hydroxyl-group-containing monomers and
vinyl aromatic monomers may be used either singly or in combination of two
or more.
In the shell, the ratio between the hydroxyl- group-containing monomer
(e.g. HEMA, HPMA) or a monomer which performs in a similar manner (e.g.
MAN, AN, or GMA), and the other copolymerizable vinyl monomers (e.g.
styrene, tribromostyrene) ranges from 2/98 to 40/60 parts by weight, and
preferably 3/97 to 30/70 parts by weight. Below 2 parts, the performance
is not improved over the vinyl aromatic homopolymer shell, and above that
level, side reactions, such as crosslinking, may occur, with adverse
effects on dispersion.
Optionally, one or more additional monomers may be added to the shell to
adjust the RI. This additional monomer is preferably an alkyl
(meth)acrylate (such as C.sub.1 -C.sub.4 alkyl (meth) acrylate, and the
like), but it can be any monomer which copolymerizes with the other two
monomers used in the core polymer and produces a terpolymer which permits
the RI of the modifier to match that of the polyesters with which it is
blended.
The additional monomer may include one or more of any of the following
monomers: acrylonitrile, methacrylonitrile, methyl acrylate, ethyl
acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl
acrylate, methyl methacrylate, ethyl methacrylate, divinyl benzene and the
like.
The resultant composition preferably has a particle size range of about 75
to about 300 nm, more preferably from about 140 nm to about 230 nm, and a
RI range of about 1.55 to about 1.60.
When the impact modifier composition containing 15-85 parts by weight of
the aforementioned rubbery core, 10-50 parts by weight of the intermediate
stage, and 5-35 parts by weight of the shell hydroxyl-group-containing
polymer (total: 100 parts by weight) is manufactured, conventional methods
for manufacturing ordinary rubber-modified polymers (e.g., ABS resin,
impact resistant polystyrene, etc.) may be effectively employed. These
impact modifiers may be prepared by emulsion polymerization. The preferred
procedure is emulsion polymerization using soaps, initiators and
processing conditions normally used for making MBS polymers, that is,
impact modifiers based on butadiene-styrene rubbers with one or more
stages of styrene or methyl methacrylate polymers. Isolation from the
emulsion can be achieved by standard procedures such as spray drying or
coagulation. For example, a polymer latex characterized by an appropriate
particle size and degree of conversion is produced by means of emulsion
polymerization (e.g. copolymerizing a hydroxyl-group-containing monomer
with another copolymerizable vinyl monomer in the presence of a
polymerized rubber latex upon which a vinyl aromatic monomer has been
polymerized or copolymerized to form an intermediate hard stage).
Further, the polymer can be prepared by a method wherein a core is
uniformly graft-polymerized with an intermediate hard stage comprising at
least one vinyl aromatic monomer, which is uniformly graft-polymerized
with a hydroxyl-group-containing monomer and another copolymerizable vinyl
monomer constituting the shell polymer.
Thus, when the impact modifier composition is manufactured, general free
radical polymerization techniques (e.g., emulsion polymerization, solution
polymerization, and suspension polymerization) may be employed so long as
the resulting impact modifier composition is characterized by a core-shell
structure wherein hydroxyl groups are preserved.
The impact modifier composition may be isolated from the reaction medium by
any of several known processes. For example, when prepared in emulsion,
the composition may be isolated by coagulation, including coagulation in
an extruder from which the water is removed as a liquid, or by
spray-drying. Additives such as thermal stabilizers and anti-oxidants may
be added to the composition prior to, during or after, isolation.
It is important that no crystallization promoter is present in the
composition since this invention is directed to compositions suitable for
producing amorphous, non-crystalline articles. If substantial
crystallization occurs in the process, the resultant articles become
opaque and brittle. In some cases, such as with pipe, foam and profile
extrusion, a small degree of crystallinity may be acceptable and can be
achieved by control of the cooling cycle. However, in most cases it is
preferred to prepare amorphous articles on standard injection molding and
extrusion equipment. The type of articles to be produced, whether it be
molded parts, bottles, films, foams, pipes, tubing, sheet or profiles,
will govern the auxiliary equipment to be employed. For instance, to
produce bottles, extrusion blow molding equipment is necessary. To produce
film, blown film equipment is necessary.
The amorphous, aromatic polyesters, such as PET, and copolyesters, such as
Eastman PETG (i.e., (poly)ethylene-co-1,4-cyclohexanedimethylene
terephthalate), of this invention include poly (C.sub.1 to C.sub.6
alkylene terephthalates), alkylene naphthalene dicarboxylates, such as
poly(ethylene naphthalene-2,6-dicarboxylate), and aromatic amorphous
polyester which contains units derived from at least one aliphatic diol or
cycloaliphatic diol or combinations of aliphatic diols and cycloaliphatic
diols and one or more aromatic dibasic acids. Examples include
polyethylene terephthalate (PET), polypentylene terephthalate, and the
like, or an aromatic copolyester which contains units derived from two
glycols (e.g., ethylene glycol, and cyclohexanedimethanol) or from two
dibasic acids (e.g. terephthalic acid and isophthalic acid). Such
polyesters may be obtained by polycondensing polyol components (e.g.,
ethylene glycol) with dicarboxylic acid components (e.g., terephthalic
acid, isophthalic acid, naphthalenedicarboxylic acid, etc.), as well as
mixtures consisting of two or more polyesters.
The modifiers and polyesters may be combined by melt blending in an
extruder. The polyesters should be dried to 0.03% moisture content. A mix
of the two components can be directly extruded or molded or the components
can be combined in an initial blending step and the pellets from this
blend can then be molded after drying to a 0.03% moisture content. The
concentration of modifier in these polyester blends can range from about 1
to about 30% by weight and preferably from about 5 to about 20% by weight.
The blends can be extruded or molded into clear parts which have very high
Dynatup impact strength, and exhibit ductile type failures and physical
aging resistance. The required modifier concentration will depend on
factors such as the molecular weight of the polyester, the impact strength
desired, and the temperature at which the final object is utilized. Below
1% modifier concentration, no significant effect is seen.
Blends should contain amorphous aromatic polyester or copolyester which has
an intrinsic viscosity of greater than or equal to 0.7 dl/g. for best
properties of molding and processing, but for some uses, lower molecular
weight polyesters may be employed. (PET or PETG may decrease in intrinsic
viscosity after melt processing; the values in the specification refer to
the polyester as supplied, prior to processing). Articles such as
containers, bottles, foam, or hollow parts may be extrusion blow molded,
extruded or injection molded from polyester blends described herein.
Blending can be accomplished by melt extrusion in an extruder at
temperatures of about 193.degree. C. to about 288.degree. C., preferably
about 204.degree. C. to about 265.degree. C. For example, a high work, two
stage screw which has a length/diameter ratio of about 24/1, and a
compression ratio of about 3.0 to 3.5 gives a very adequate dispersion of
the modifier in the polyester. A dwell time in the extruder of 1 to 5
minutes is adequate to insure complete mixing or dispersion under most
conditions but of course lower and higher dwell times can certainly be
used. Preferably the strands produced by extruder blending are pelletized
and dried to a moisture content of less than 0.03 percent before molding.
The ingredients used to make the composition of the invention are dispersed
uniformly and it has been found that melt blending the ingredients, by
using such equipment as a melt extruder (e.g., single screw extruders or
twin screw extruders) in a separate step prior to molding is desirable.
The blended product may be pelletized (i.e., the extruded strand is
quenched and cut), dried and used for subsequent molding purposes.
Other additives known in the art may be included in the composition at
about 1 to about 30% by weight. These other additives may include
antioxidants, flame retardants, reinforcing agents such as glass fiber,
asbestos fiber and flake, mineral fillers, stabilizers, nucleating agents,
ultraviolet light stabilizers, heat and light stabilizers, lubricants,
dyes, pigments, toners, mold release agents, fillers, such as glass beads
and talc, and the like. Minor amounts of other polymers (i.e. about 1 to
about 10 percent by weight) can also be incorporated in the present
composition, such as polyamides or polycarbonates. Most of these additives
will adversely affect clarity. The additives listed above such as
antioxidants, thermal stabilizers, fillers, pigments and flame retardant
additives may be used in the composition of this invention provided they
do not exert any adverse effect on the impact strength or clarity. It is
preferred not to have glass fiber reinforcement in clear article
applications or any additive which would decrease transparency. It is
highly preferred that clear articles are produced.
The polyesters must be thoroughly dried prior to melt processing to
minimize the rapid hydrolytic degradation known to occur at processing
temperatures and to reduce molecular weight. The modifiers of the present
invention are much less sensitive to hydrolytic degradation than the
polyesters. Higher than necessary melt temperatures should be avoided
during processing to keep the impact strength as high as possible. Melt
cooling should be carried out as rapidly as possible to prevent polyester
crystallization and the loss of clarity.
Aromatic amorphous polyesters are quite sensitive to embrittlement from
physical aging, but this limitation is overcome by the modifiers herein
(see Table 1). Therefore, polyester blends will now be able to compete
successfully with polycarbonate, cellulosics, impact modified polyvinyl
chloride, and the like for a broad range of applications where high
clarity and toughness are needed in the absence of exceptional heat
resistance.
The preferred poly(alkylene terephthalates) are polyethylene terephthalate
(PET) and copolyesters of PET. Blends with other polyesters are also
suitable. For example, blends of two or more polyesters may also be used,
with polyester blends which have poly (ethylene terephthalate) being
preferred.
EXAMPLES
The following examples and comparative examples are presented to illustrate
the invention, but the invention should not be limited by these examples.
All parts and percentages are by weight unless otherwise indicated. The
following abbreviations are employed in the examples:
Bd=butadiene
S=styrene
HEMA=hydroxy ethyl methacrylate
DVB=divinyl benzene.
Apparatus and General Procedure
Modifier compositions are melt blended with APET (Shell 8387) using a twin
screw extruder. The clear amorphous strands are pelletized and the
accumulated product recrystallized before re-extrusion into 0.0762 cm
thick sheet. This sheet is then evaluated for impact strength at
23.degree. C. using the Dynatup impact test (ASTM-D3763-93). The test is
repeated on sheet test samples that have heat aged at 60.degree. C. over a
period of ten days to establish the relative retention of impact strength
of the modified APET sheet.
Sheet samples are tested for light transmission and haze according to
ASTM-D-1003.
The blue/yellow hue of the sheet samples are measured two ways. First, the
"b" value of the Hunter L,a,b scale is measured. The Hunter b value is a
measure yellowness-blueness, and the procedure for determining this value
is provided in Instruction Manual: HUNTERLAB TRISTIMULUS COLORIMETER MODEL
D25P-9 (rev. A). The second parameter measured is referred to as the
Scattered Yellowness Index. The Scattered Yellowness Index is calculated
according to the Yellowness Index procedure of ASTM-D-1925, using diffused
(scattered) Transmission values instead of total Transmission values.
Example 1
A modifier based upon Example 12 of U.S. Pat. No. 5,321,056, with minor
modifications, was prepared according to the following procedure:
Charge 34.666 parts deionized water and 0.109 parts acetic acid to a
stainless steel reactor capable of withstanding 200 psi (1.38 mPa)
pressure. Begin stirring at 100 rpm and heating to 95.degree. C. while
sparging with nitrogen for 30 minutes. At 95.degree. C., turn off sparge
and add 3.182 parts (33% solids) of a Bd/S (at a ratio of approximately
70:30) seed emulsion. Also add 2.016 parts of a 5% aqueous solution of
sodium formaldehyde sulfoxylate, then rinse both with about 2.092 parts
deionized water. Evacuate the reactor to 260 mm Hg. At 95.degree. C.,
begin feeding butadiene [12.824 parts]., a mix of monomers [12.121 parts S
and 0.252 parts DVB with a deionized water rinse of 1.356 parts], Dowfax
2A1 soap solution [3.528 parts at 10% solids] to the reactor over a 5 hour
period . The 2% aqueous t-butyl hydroperoxide solution [4.143 parts] is
added over 7.25 hours. The soap and tBHP solutions are uniform constant
rate feeds. The monomer mix and Bd feeds change each hour as follows:
First hour=0.00076 parts/minute S/DVB and 0.00008 parts/minute Bd
Second hour=00055 parts/minute S/DVB and 0.00029 parts/minute Bd
Third hour=00042 parts/minute S/DVB and 0.00042 parts/minute Bd
Fourth hour=00025 parts/minute S/DVB and 0.00059 parts/minute Bd
Fifth hour=00008 parts/minute S/DVB and 0.00076 parts/minute Bd
Continue the 2% aqueous t-butyl hydroperoxide solution feed after the
monomer feeds and rinse are done. When all feeds are finished, hold 0.5
hours at 95.degree. C. Cool the reactor to 62.degree. C. and vent to
atmospheric pressure.
The shell is prepared by adding 0.657 parts of a 5% solution of sodium
formaldehyde sulfoxylate to the reactor [rinse with 0.562 parts deionized
water]. At 60.degree. C., begin feeding a mix of S [16.071 parts] and HEMA
[2.169 parts] for 1.5 hour at a constant rate. Also begin feeding 1.369
parts of a 2% solution of t-butyl hydroperoxide for 1.5 hour at constant
rate. After the 1.5 hour feed is in and rinse [1.264 parts deionized
water] is added, chase with 2% solution of t-butyl hydroperoxide solution
[1.094 parts] for four hours at constant rate, and 4 shots of a 5%
solution of sodium formaldehyde sulfoxylate [0.525 parts total; 0.1313
parts per shot at 0, 1, 2 and 3 hours]. Add 0.575 parts sodium hydroxide
solution [0.2% solid] and then add a 50% solids emulsion of Irganox 245
[0.180 parts], tris nonyl phenyl phosphite [0.180 parts] and dilauryl
thiodipropionate [0.540 parts]. Cool the batch to 40.degree. C.
The RI of the resulting modifier composition was measured to
1.565.+-.0.002, using ASTM-D-542.
Example 2
A composition within the scope of the present invention was made according
to the following procedure:
Charge 23.319 parts deionized water to a stainless steel reactor capable of
withstanding 200 psi (1.38 mPa) pressure. Add 1.182 parts of a 5% aqueous
solution of sodium formaldehyde sulfoxylate. Begin stirring at 130 rpm and
heating to 85.degree. C. while sparging with nitrogen (0.283 scmh) for 30
minutes. At 85.degree. C., turn off sparge and add 3.590 parts (33%
solids) of a Bd/S (at a ratio of approximately 70:30) seed emulsion, rinse
with about 0.507 parts deionized water. Evacuate the reactor to 362-414 mm
Hg. Begin feeding an emulsified mix of monomers, soap and water to the
reactor over a 4.75 hour period. The emulsified monomer mix contains:
14.221 parts S, 0.269 parts DVB, 0.213 parts sodium dodecyl benzene
sulfonate soap, 6.606 parts deionized water [and 1.014 parts deionized
water rinse]. Feed rates for the emulsified monomer mix change over time:
1.75 hours at 0.1349 parts/minute, 1.25 hours at 0.0766 parts/minute and
1.5 hours at 0.0152 parts/minute. Other feeds are started the same time as
the emulsified monomer mix: Bd [12.368 parts] is fed over time starting at
1.75 hours after the start of the emulsified monomers [1.25 hours at
0.0522 parts/minute then 1.5 hours at 0.0938 parts/minute]; 2.377 parts of
a 10% aqueous solution of sodium dodecyl benzene sulfonate solution is fed
at a constant rate of 0.0088 parts/minute for 4.5 hours; 1.774 parts of a
5% aqueous t-butyl hydroperoxide- solution is added at a constant rate of
0.00657 parts/minute for 4.5 hours. At the end of feeds, rinse with 1.267
parts deionized water.
After rinse is added, charge 0.625 parts of a 5% solution of sodium
formaldehyde sulfoxylate to the reactor. Begin feeding an emulsified
styrene charge for 2 hours at 0.1373 parts/minute [contains: 11.660 parts
S, 0.153 parts sodium dodecyl benzene sulfonate, 0.035 parts t-butyl
hydroperoxide, 4.628 parts deionized water (and 0.760 parts rinse of
deionized water)].
After rinse is added, charge 0.070 parts of 5% solution of t-butyl
hydroperoxide and 0.070 parts of 5% solution of sodium formaldehyde
sulfoxylate to the reactor. Hold for 1 hour. Vent the reactor to
atmospheric pressure.
Begin a constant rate feed of emulsified monomers for 1 hour: 6.142 parts
S, 0.840 parts HEMA, 0.014 parts DVB, 0.021 parts t-butyl hydroperoxide,
0.101 parts sodium dodecyl benzene sulfonate, 3.191 parts deionized water
(rinse with 0.507 parts deionized water). Feed shots of 5% solution of
t-butyl hydroperoxide [1.460 parts] and 5% solution of sodium formaldehyde
sulfoxylate [1.016 parts] over 6 hours. A 50% solids emulsion of Irganox
1010 [0.098 parts], Irganox 245 [0.098 parts] and dilauryl
thiodipropionate [0.504 parts] is then added. Cool the batch to 60.degree.
C.
The RI of the resulting modifier composition was measured to
1.570.+-.0.002, using ASTM-D-542.
Example 3
Charge 21.794 parts deionized water to a stainless steel reactor capable of
withstanding 200 psi (1.38 mPa) pressure. Add 1.411 parts of a 5% aqueous
solution of sodium formaldehyde sulfoxylate. Begin stirring at 175 rpm and
heating to 85.degree. C. while sparging with nitrogen for 30 minutes . At
85.degree. C., turn off sparge and add 3.934 parts (35% solids) of a Bd/S
(at a ratio of approximately 70:30) seed emulsion, rinse with about 0.519
parts deionized water. Evacuate the reactor to 362-414 mm Hg. Begin
feeding an emulsified mix of monomers, soap and water to the reactor over
a 5 hour period. The emulsified monomer mix contains: 23.335 parts S,
0.321 parts DVB, 1.738 parts Dowfax 2A1 soap [20% solid], 9.392 parts
deionized water. Feed rates for the emulsified monomer mix change over
time: 2 hours at 0.1512 parts/minute, 1.5 hour at 0.0338 parts/minute and
1.5 hours at 0.1512 parts/minute. Other feeds are started as follows: Bd
[8.422 parts] is added in a shot plus a feed--at 1 hour after the start of
the emulsified monomers a shot of 0.804 parts is added, then a 1.5 hour
feed at 0.0846 parts/minute is started at 2 hours after the start of the
emulsified monomers; 1.847 parts of a 20% aqueous solution of Dowfax 2A1
soap is fed at a constant rate of 0.00616 parts/minute for 5 hours; 2.117
parts of a 5% aqueous t-butyl hydroperoxide solution is added at a
constant rate of 0.00504 parts/minute for 7 hours. At the end of monomer
feeds, rinse with 1.038 parts deionized water. Continue feeding 5% aqueous
t-butyl hydroperoxide-solution for 2 hours. Hold 30 minutes. Pressure
should be about 1.6-1.8.times.10.sup.5 Pa. Vent to atmospheric pressure.
Charge 0.311 parts of a 5% solution of sodium formaldehyde sulfoxylate to
the reactor. Begin feeding an emulsified styrene mix for 1 hour at 0.179
parts/minute [contains: 7.161 parts S, 0.527 parts Dowfax 2A1 soap, 3.051
parts deionized water (and 0.519 parts rinse of deionized water)]. Also
feed 0.435 of a 5% solution of t-butyl hydroperoxide for one hour at
0.00725 parts/minute.
After 1 hour feed is in and rinse is added, begin a constant rate feed of
emulsified monomers for 1 hour [6.287 parts S, 0.859 parts HEMA, 0.015
parts DVB, 0.527 parts Dowfax 2A1 soap [20% solids], 3.051 parts deionized
water] (rinse with 0.519 parts deionized water)] and also a 1 hour
constant rate feed of 0.435 parts of a 5% solution of t-butyl
hydroperoxide solution. After the feeds are in, feed 0.435 parts of 5%
solution of t-butyl hydroperoxide solution for one hour at constant rate.
A 50% solids emulsion of Irganox 1010 [0.100 parts], Irganox 245 [0.100
parts] and dilauryl thiodipropionate [0.516 parts] is then added. Cool the
batch to 60.degree. C.
The RI of the resulting modifier composition was measured to be
1.577.+-.0.002, using ASTM-D-542.
TABLE 1
______________________________________
Modifier Modifier Dynatup Impact Strength (J/m .times. 10.sup.2)
Example Content Time in Oven at 60.degree. C. (days)
No. (%) 0 1 3 5 10
______________________________________
control 0 246 80.1 81.1 37.9 49.1
1 5 353 280 278 289 323
2 5 257 251 268 247 258
3 5 263 185 185 146 116
1 10 428 307 356 324 381
2 10 369 288 308 290 289
3 10 337 282 193 223 168
______________________________________
Table 1 reports the measured impact strength of APET blends containing the
modifiers of Examples 1 through 3, compared to the impact strength of a
control sample (i.e., Shell 8387 APET resin without the addition of
modifier). The results illustrate that compositions within the scope of
the present invention, such as the modifiers of Examples 2 and 3, provide
the excellent impact resistance of compositions reported in U.S. Pat. No.
5,321,056.
TABLE 2
______________________________________
Modifier
Modifier Scattered
Example
Concentration
% % Yellowness
No. (%) Transmission
Haze b Index
______________________________________
control
0 89.5 0.8 0.8 -21
1 5 87.2 2.6 4.6 -226
2 5 88.5 2.8 3.1 -197
3 5 87.8 3 1.8 2
1 10 87.2 3.3 4.2 -224
2 10 88.9 4 2.3 -178
3 10 88.2 3.6 1.6 -17
______________________________________
Table 2 reports the measured optical properties of APET blends containing
the modifiers of Examples 1 through 3, compared to the optical properties
of the control sample. The results illustrate that compositions within the
scope of the present invention, such as the modifiers of Examples 2 and 3,
provide dramatically improved optical properties over the compositions
reported in U.S. Pat. No. 5,321,056.
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